Optical processing of vector and matrix data is known for its potential high effective computational performance capabilities and its natural adaptability to computationally intensive image processing. Images, or other spatially relatable data, may be treated as matrices composed of rastor or vector scans of data elements that, at their real or effective resolution limit, are generally referred to as pixels. An ordinary image is typified by an analog picture frame taken as a cross section of an optical beam formed of a continuous series of such images. Each analog image frame typically contains an effectively continuous spatially distributed array of pixel data. Alternately, discrete matrix data may be impressed onto a data beam by spatially modulating the cross section of a data beam in terms of, for example, either its localized intensity or polarization vector.
In any case, optical processing is of great potential value due to its fundamentally parallel processing nature. The parallelism, of course, arises due to the processing of complete images at a time. As each pixel is a separate datum, the volume of data processed in parallel is generally equivalent to the effective resolution of the image. Additionally, optical processing has the virtue of processing data in the same format that it is conventionally obtained. Typically, and for such applications as image enhancement and recognition, the data to be processed is generally obtained as a single image or as a rastor scan of an image frame. Potentially then, an optical processor may receive data directly without conventional or other intermediate processing. Since the informative value of image data increases with the effective resolution of the image and the number of images considered, the particular and unique attributes of optical processing become quite desirable.
Conventionally, optical processing is performed by projecting an image to be processed through a selected spatial mask onto an appropriate optical detector. The mask itself is, in its simplest form, only an image fixed in a film. Even as such, relatively complex optical processing computations may be performed.
Optical processor projection systems, however, generally require a variety of highly specialized components including arc lamps as illuminating point sources, collimating and focusing lenses, polarizing and polarization rotation plates, beam splitters, and mirrors. In addition to their respective fabrication complexities, these components must be assembled and maintained, often in critical alignment, spatially separated from one another. Consequently, the optical processing apparatus is large and bulky, sensitive to its environment, particularly in terms of vibration and contamination, and specifically limited to performing one or only a few quite closely related optical processing calculations.
In addition to photographic films, a temporally variable mask for optical processors has been realized as a two-dimensional spatial light modulator (SLM) that, through electronic activation, effects selective alteration of the spatially distributed data impressed on a data beam by the mask. A typical two-dimensional (2D) SLM is realized through the use of a photo-electrically activated reflective type liquid crystal light valve which may be coupled to a cathode ray tube. Aside from the inefficiency of the dual serial electric-to-optical conversion of the image, such 2D SLM devices perform well for many applications within specific limits. Unfortunately, these performance limits include a relatively slow liquid crystal light valve response time of typically greater than 10 milliseconds. This naturally directly impacts the high speed processing capability of an optical processor. Additionally, the use of this type of mask requires further focusing, beam splitting and support components with the end result being a mechanically complex optical processor.
Two-dimensional SLM masks have also been realized in the form of a solid electro-optic element activated by a two-dimensional spatially distributed array of electrodes. The modulating image is effectively formed by separately establishing the voltage potential of each of the electrodes at an analog corresponding to their respective intended data values. As may be well expected, the complexity level of such a two-dimensional SLM increases proportionally to the square of its pixel resolution (N). Complexity further increases where the N.sup.2 electrodes must be independently addressable to permit operation at data rates sufficiently high to be of utility in optical data processing (for instance, for N=1000, one has to address 1 million electrodes). The current level of fabrication technology, unfortunately, stands as a practical barrier to the reproducible fabrication of even moderately high resolution independent pixel addressable two-dimensional SLM devices. Alternately using a low effective resolution mask would directly impact the high speed data processing capabilities of the optical processor.